Web tension control system



Dec. 10, 1968 A. A. PINTO ETAL WEB TENSION CONTROL SYSTEM 2 Sheets-Sheet 1 Filed Feb. 4. 1966 O mmm mmhmai INVENTORS ALBERT A. PINTO BY KENNET L. new J 1M AG NT 2 Sheets-Sheet 2 \N L RN I A. A. PINTO ETAL WEB TENSION CONTROL SYSTEM Dec. 10, 1968 Filed Feb; 4, 1966 \NVENTORS ALBERTA. PINTO KENNETH .DEW

A ENT United States Patent O ABSTRACT OF THE DISCLOSURE An apparatus in which a web of material being moved through various steps for coating, lamination, perforation, or other treatment is automatically kept at suitable constant tension to prevent wrinkling, breaking or undue stress by utilizing a servomechanism system or feedback control means. The latter detects the difference between a reference signal and some function of a controlled variable signal to provide an actuating error signal which is fed back to a suitable control element which instantly responds to correct the variation in the tension of the moving web without necessitating contact with the material of the web in carrying out the correction.

Many devices have been designed to automatically control tension in a moving web. Most of these are extremely complex and consequently very sensitive to minute inaccuracies in construction. They also require a great amount of maintenance to keep them functioning properly. Then too, most previous devices do not lend themselves to a variety of applications for, in general, they have been designed for a particular operation, thus limiting their versatility. Cost has also been a prohibitive factor in the widespread use of the highly sensitive tension control devices. This present invention, though a highly sensitive tension control device, eliminates many of the above described undesirable features as will be pointed out in further detail.

Therefore, the primary object of the invention is to provide an automatic device for controlling tension in a moving web of material.

A further object of the invention is to provide an automatic tension control device that will respond instantaneously to a deviation in tension of the moving web from a predetermined value.

Another important object of the invention is to provide an automatic tension control device that will not only control tension at the unreeling and reel winding stations. but will also be capable of operating between conversion stations in a web system.

A still further object of the invention is to provide an automatic tension control device which is highly sensitive in controlling slight changes in web tension without requiring the use of complex equipment.

Yet another object of the invention is to provide an automatic tension control device in which the desired tension can be varied while the system is in operation.

A further object of the invention is to provide a programmed tension control device which will automatically regulate and vary progressively or otherwise as desired the tightness with which the web material is wound onto a roll.

Other objects and unique features of the invention will be apparent from the following description and claims taken in connection with the accompanying drawings in which:

FIGURE 1 is a diagrammatic representation which includes a schematic wiring diagram of the tension control apparatus embodying the features and principles of the invention in operation with a web supply mechanism;

FIGURE 1-A is a detailed cross sectional view taken along line lA-lA of the variable pitch pulley shown in FIGURE 1.

FIGURE 2 is a diagrammatic representation including a schematic wiring diagram of the tension control apparatus as used in conjunction with a programmed tension control device in operation with a web windup mecha- IllSIll.

The following description will make reference to the accompanying drawings which are for the purpose of illustration only and do not limit or define exactly the structural details of the invention.

Referring now to the drawings, there is shown in FIG- URE 1 a diagrammatic representation of a strip or web of material 1 in the process of being withdrawn or unwound at a constant linear speed from a storage roll 2. The storage roll is fixed to spindle 3 and is being driven by a peripheral surface drive mechanism 4 which is well known in the art. Drive mechanism 4 comprises a triangular plate 5 with two guide pulleys 6 and 7 and drive pulley 8, the pulleys being rotatably mounted at the corners of plate 5. Passing around all three pulleys is an endless drive belt 12 with the pulleys 6 and 8 positioned so as to provide the belt with a suitable angle of drive wrap applied to the storage roll 2. As seen in FIGURE 1 triangular plate 5 is pivoted on fixed shaft 14 and is supported by piston shaft 15 which is pivotally connected to plate 5 by a pin 16. Piston shaft 15 is actuated by air cylinder 13 providing a constant upward force thus lifting the surface drive mechanism 4 into continuous peripheral driving position. Contact between drive belt 12 and storage roll 2 is maintained at a constant predetermined pressure by operation of air cylinder 13 which also forces the drive belt 12 to follow the contour of the storage roll 2 as the diameter of the latter decreases due to the unwinding of the sheet material on the roll. FIG. 1 also shows the surface drive mechanism 4 operating with a greatly depleted storage roll 2' (dot and dash outline).

Speed control of drive belt 12 and consequently the rate at which the web material 1 unwinds from the storage roll 2, is controlled by variable speed motor 11 which is coupled to drive pulley 8 by endless belt 10. Speed 'variation of variable speed motor 11 provides the means for controlling the tension in moving web 1.

VARIABLE SPEED MOTOR CONTROL As seen in FIGURE 1 the web of sheet material 1 unwinds from storage roll 2 and passes about guide roller 17 and then under a floating roller 18. From the roller 18 the web 1 passes about a driven roller 20 which pulls the material at a constant rate by means of driven roller 21 which bears against the web of material as it passes around roller 20. Driven rollers 20 and 21 are rotated synchronously at the same predetermined speed thus supplying the material to a processing station 29 at a constant linear velocity. The rollers are mechanically linked as shown in the dot and dash outline 20' and 21.

With the sheet material 1 being pulled at a constant rate by rollers 20 and 21, tension variation in the web material will be inevitable between the supply roll 2 and the pull rollers 20 and 21 unless the rotational speed of the supply roll 2 is closely controlled so as to regulate the rate of unwinding of the material from the roll. Thus, tension control in the moving web is being obtained by making the supply roll rotational speed directly proportional to a desired tension in the moving web. This is accomplished by a mechanical sensing system in combination with an electrical feedback correcting system as shown in FIGURE 1. The mechanical sensing system comprises the floating roller 18 fixed to a sensing arm 22 which is rotatably mounted on a pivot point 23. Fixed at one end to sensing arm 22, at connection point 24, is a tension spring 25 and suspended intermediate of the pivot 23 is a load 26 which provides a predetermined downward moment about pivot point 23 acting on sensing arm 22. The value of this moment is predetermined to directly oppose the upward moment about pivot point 23 caused by the web of material forming a loop 19 about the floating roller 18. Under ideal operating conditions the opposing forces will cancel each other and sensing arm 22 (FIGURE 1solid outline) will remain in a horizontal and relatively stable position. Any desired value of tension in the moving web of material can be obtained by varying the load on tension spring 25. Such a change in load will vary the opposing upward moment produced by the moving web of material and consequently change the tension in the material. The opposing forces will determine the position of sensing arm 22, which, as stated previously, is free to move about pivot point 23. As sensing arm 22 changes position due to variations of the opposing moments resulting from changes of tension in the moving web, it will pivot about point 23, consequently changing the position of the follower pulley 27 fixed to its opposite end. Follower pulley 27 is in contact with an endless belt 28, which passes about a fixed pitch pulley 30 and a variable pitch pulley 31. Fixed pitch pulley 30 is driven from roller 20 at the same rotational speed of the latter by means of drive belt 32. Thus, the speed of pulley 30 will be directly proportional to the speed of pull rollers 20 and 21. Consequently belt 28 which passes around pulley 30 will also travel at a speed directly proportional to that of pull rollers 20 and 21, the speed of which will vary according to the demands of the web receiving equipment or the demand from processing station 29. As belt 28 passes about variable pitch pulley 31 the pulley is driven at a speed dependent upon the distance of the belt from the center of shaft 33 onto which the pulley 31 is fixed (FIG. l-A).

As shown in FIGURE lA, variations of rotational speed of pulley 31 may be obtained by forceably changing the position of belt 28 relative to shaft 33. For instance, to obtain a greater rotational speed of pulley 31, belt 28 is forced inward towards the shaft causing the side plates 35 of pulley 31 to move in opposite directions along shaft 33 which permits belt 28 to change its position and consequently the pitch surface and effective radius of pulley 31. Thus, with belt 28 changing its position and causing a change in effective radius but still maintaining the same speed, pulley 31 will be driven at a greater rotational speed, the increase of which will be directly proportional to the change of the effective radius. The converse is effected when the belt 28 is forced out-' wardly, thus increasing the effective radius and pitch surface of pulley 31. The pulley side plates 35 (FIGURE 1A) are held in position by compression springs 36 which permit lateral in and out movement of said plates 35 on the shaft 33.

Coupled directly to shafts 33 and 34 (as shown in FIG. 1) are servo-motors 38 and 37 respectively and which consequently generate a constant signal directly proportional to the speed at which they are being driven. Under desired tension conditions of the moving web, the sensing arm 22 will dispose the follower pulley 27 in a neutral position (shown in solid outline) againat drive belt 28 so as to place the belt around variable pitch pulley 31 with a pitch surface and elfective radius equal to that of fixed pitch pulley 30. With both pulleys having the same effective radius, variable pitch pulley 31 will be synchronized with pulley 30 which is being driven by the pull rollers 20 and 21. Thus with both pulleys 30 and 31 rotating at the same speed their respectively linked servomotors 37 and 38 will generate signals precisely identical in value causing a zero differential of electrical potential between the two servomotors. A zero differential will only occur when tension in the movin Web is at a predetermined desirable value thus requiring no correction. As soon as a tension variation occurs, floating roller 18 will change position to compensate for an increase 18a or decrease 18b in the length of the loop 19 formed by the web 1. This change of position of floating roller 18 not only compensates for a change in tension of the moving web but also initiates corrective procedures to alleviate the cause of the variation in tension. This corrective procedure is commenced instantaneously with the initiil change of position of sensing roller 18 for as sensing roller 18 changes position sensing arm 22 and follower pulley 27 will simultaneously change position to 27a or 27b. This change of position of follower pulley 27 which is directly proportional to the variations of tension in the web will change the position of belt 28 and consequently the effective radius and pitch surface of variable pitch pulley 31.

The servomotor 38 which is called the slave servo generates an which is directly proportional to the actual tension in the moving Web.

Servomotor 37 which is called the master servo and which is linked and driven by fixed pitch pulley 3t}, generates an directly proportional to the varying demands of the processing stations or web receiving equipment. The difference of the two signals generated by the master and slave servos will be proportional to the difference in actual and desired tension in the moving web and will be measured by the voltage sensitive device 40. The difference or error signal will have a magnitude and a plus or minus direction which will be received by the frequency alternator 41 through the voltage sensitive device 40. As the frequency alternator 41 converts the generated signal into a corrective frequency it is then applied to the variable speed synchronous motor 11, subsequently increasing or decreasing the rotational speed of supply roll 2 thus correcting the rate at which the web material 1 is being unwound. In this manner, a change of material unwinding rate will correct the error in tension and return sensing arm 22 back to a neutral position with both master and slave servomotors rotating at precisely the same speed to return the error signal to a zero value. This correcting process is not a step function but rather a continuous correcting operation changing with uncontrolled variations of tension from a desired value and meeting the demands for varying rates of web material.

The windup of sheet material from a processing operation as shown in FIGURE 2 will also require tension control in order to maintain proper operating conditions. The processed sheet material 42 is drawn from the processing station 29 by driven pull roller 43 which pulls the material at a constant linear velocity. To maintain the material in contact with the pull roller 43 to provide a constant drawing of material from the processing equipment, pinch roller 44 bears against the web of material as it is drawn by the pull roller. The pinch roller 44 maintains a proper pressure against the pull roller 43 and theuweb therebetween by means of spring 45. From the pull roller 43, the web of material 42 passes under sensing roller 18 and then about guide pulley 46 from which the material is drawn onto driven spindle 47 to form the beginning of a roll of material 48.

Spindle 47, as shown in FIG. 2, is driven by sychronous motor 50 by means of drive belt 49. The rotational speed of the spindle 47 is dependent upon the length of the loop of material 19 in the moving web of material as sensed by roller 18 and sensing arm 22, the operation of which is similar to that previously discussed for the system shown in FIG. 1.

The tension in the moving web of material 42 will also determine the tightness of wrap of the web material being wound around spindle 47. Precise control of web tension is especially important, for example, in winding of plastic film which would require a more tightly wound roll near the spindle with a progressively looser winding towards the outer circumference. This can be effected by utilizing the same tension control system as described in FIG. 1 with a programmed change of desired tension to be applied through spring 25. A programmed variation of tension in the moving web of material 42 is obtained by means of a plate cam 56 fixed to shaft 57 which is linked to and driven by shaft 47. The cam is rotated by suitable driving gears 58 to make one complete revolution for every completely wound roll of material 48. As cam 56 rotates, it actuates follower 54 which is in contact with the cam contour. The displacement of follower 54 is in .a vertical plane and designed to rock the lever arm 51 from minimum to maximum in one 360 rotation of the cam 56. The follower 54 is free to rotate on shaft 55 which is fixed to rocker 51. The rocker 51 which is free to oscillate at its fulcrum 53 provides the means of transmitting the follower displacement to spring 25 which is fixed to the opposite end of rocker 51 at point 52. As previously discussed for the system in FIG. 1, spring 25 provided the means for setting a desired tension in the moving web of material by suspending the required load from its end. By connecting the end of spring 25 to the rocker arm 51 at point 52 the load is replaced by a varying force equivalent to the follower displacement. This is illustrated in the dot-and-dash outline 51' of FIG. 2. As cam 56 is rotated during the winding cycle to position 56, follower 54 will be gradually displaced to posit-ion 54'. Consequently rocker 51 is pivoted about its fulcrum 53 to position 51'. Any change in position of rocker 51 will simultaneously displace connection point 52 to position 52' which will result in a displacement of spring 25 and consequently effect a downward force applied to sensing arm 22 by the spring. This change in the downward force being applied to sensing arm 22 will cause a directly proportional change in tension in the moving web of material 42. A change in tension as previously stated will directly change the tightness in which the sheet material will be wound into a roll. Thus, any variation of tightness can be obtained by varying the contour of the plate cam 56. The previous reference to plastic film which would require a more tightly wound roll near the spindle with a progressively looser winding towards the outer circumference can be easily obtained by forming the plate cam 56 so as to impart a maximum rise of follower 54 at the beginning of the winding cycle with a gradual decline thereafter. This will effect a maximum tension in the moving web of material at the beginning of the cycle which will consequently provide a more tightly wound roll of plastic film near the spindle as required. A gradual decrease in tension will then provide a looser winding toward the peripheral surface of the roll.

It will be understood that various changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What we claim as our invention and desire by Letters Patent is:

1. An apparatus for automatically controlling tension in a moving web of sheet material comprising in combination:

(a) means for rotating a roll of said web material, in-

cluding motor means;

(b) means for providing linear velocity to said material including .a pair of rollers engaging the opposite sides of said material;

(c) means for setting a desired value of tension in said moving web of material in direct proportion to the rotational speed of said roll of web material includto secure (d) a loop of web material depending between said roll .and said linear velocity rollers, a roller floating in said loop, an endless belt, a fixed pitch pulley and a variable pitch pulley about which said endless belt travels, said pulleys rotating at the same speed when the tension in the moving web is at a predetermined desirable value not requiring correction;

(e) a fulcrumed sensing arm means having a following pulley at the opposite end thereof from said floating roller, to the latter of which the other end of said arm is pivoted, said arm yieldably maintaining the roller and pulley in contact respectively with the loop of the web and the endless belt whereby variation in the speed of the material effecting a movement of said loop will vary the speed of operation of said variable pitch pulley;

(f) slave servomotor means associated with said variable pitch pulley for generating an E.M.F. signal directly proportional to the tension in the web as detected by the movement of said floating roller;

(g). master servometer means associated with said fixed pitch pulley for generating an signal directly proportional to the desired tension in the web of material, the diflerence in the two signals generated by said slave and master servomotor means being proportional to the difference in actual and desired tension in the moving web;

(h) voltage sensitive means in circuit with said slave and master servomotor means for providing an error signal in magnitude and plus or minus direction, and

(i) frequency alternator means for converting said error signal into a corrective frequency for controlling the operation of said motor means whereby a continuous correcting operation, changing with uncontrolled variations of tension from a desired value and meeting the demands for varying rates of web material tension is provided.

2. An apparatus according to claim 1 wherein said means for rotating said web of material includes:

(a) pivoted triangular plate means, guide and drive pulleys mounted at the camers of said plate means and over which pulleys passes a drive belt;

(b) synchronous motor means for driving said belt,

and

(c) air cylinder means including a piston shaft pivoted to said plate means and operable through the air cylinder to raise and lower said plate means to maintain the drive belt in contact with the periphery of said roll of material.

3. An apparatus according to claim 1 wherein said sensing arm means includes tension spring load means for providing a predetermined downward movement about the fulcrum of said arm means.

References Cited UNITED STATES PATENTS 2,984,429 5/ 1961 Huck 242-75.1 3,148,816 9/ 1964 Martin et al 226-95 3,223,906 12/ 1965 Dinger 318-7 3,283,228 11/1966 Asseo 318-7 ORIS L. RADER, Primary Examiner. B. A. COOPER, Assistant Examiner.

U.S. Cl. X.R. 

